The present invention relates to photo reprographic copying machines and particularly to dry magnetic developing apparatus utilized therein.
In copiers utilizing dry magnetic developing apparatus, there has been a constant search for ways to achieve significant improvements in the copy output quality. Copy quality comes largely from the developing apparatus, and more particularly from the mechanisms involved which distribute and feed the developer material to the exposed photoconductor image carrier within the copiers process system.
The photoconductor is typically coated upon a holding member such as a drum, a flexible endless web, or an advancible film type carrier device with accommodating spools which are stored within a support cylinder. When the copier is activated by an operator, the photoconductor is electrically sensitized in advance of reception of an optically transmitted image of an illuminated object. The object is typically any original document which is placed face down upon a glass platen, the platen appropriately located on an upper working surface of the copier. The original is illuminated by stationary or reciprocating scanning apparatus located within the confines of the machine and positioned beneath the glass platen. During the illumination-scanning function, the image of the original is transmitted through the copiers optical system in a fashion not unlike the imaging system of a camera. During this process, the image is received on the photoconductor, and carried thereon to an area encompassing a portion of the photoconductor called the development zone, the latent exposed image is visibly developed by developer material which is electrostatically attracted to the previously exposed image.
The photoconductor continues on a predetermined path away from the development zone towards a transfer area. For every exposed image of an original document, a piece of copy paper is provided from a supply stack so that each sheet is transported, registered, and held against the moving photoconductor. While progressing through the transfer zone, an appropriately mounted corona, or transfer roller, applies an electrical charge through the copy sheet, thereby causing physical transfer of the developed image to the sheet.
Immediately after the leading edge of the copy sheet has received the leading end of the image, a detacking mechanism forces the leading end of the sheet away from the photoconductor. Then a separate transport system carries the copy sheet towards a fusing or fixing apparatus where radiant energy, heated hot roller pressure, or cold pressure of substantial magnitude is exerted upon the sheet as it passes through the apparatus. Immediately after fixing, the copy sheet is delivered in a sheet receiving tray to the machine operator.
The developing apparatus described in prior art typically has been provided with various instrumentalities designed to distribute, mix, circulate and apply developer material at the process development zone. In later prior art, an emphasis towards multiple developer applicator rolls has been demonstrated. The multiple applicator rollers are provided in various geometric variations and combinations that encompass the development zone. These rollers circulate the developer material through the developing apparatus and development zone in such a manner so that the developer is continuously passed along in a chain-like fashion brush form.
In addition, there are magnets mounted inside the rollers which may be either fixed or rotating. The magnets provide a substantial force in the form of magnetic flux which attracts the developer material unto the outer cylindrical surface of each applicator roller. The developer material is caused to stand up under influence of the magnetic flux so that it bristles radially outwards over a segment of the cylindrical roll surface, the bristle brush then engaging the photoconductor for the purpose of providing the toner constituent from the developer at the charged, exposed image.
When multiple applicator rollers are used in the developing apparatus, there is a better opportunity for development, since the multiple brushes present developer material to a given charged photoconductor image area over an extended time and distance. Ultimately, the net result in copy quality in terms of overall development is immediately seen when large solid areas representing the solid areas of an original are developed.
Similarly, there is also prior art which describes use of belt developer material applicator devices for conveying and applying the developer in a brush-like manner to the charged image on a photoconductor member. Such a system which utilizes belts is described henceforth in a brief abstract of an earlier issued patent.